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Add ranget drop and skip methods #4347

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Merged
merged 3 commits into from
Mar 8, 2019
Merged

Add ranget drop and skip methods #4347

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b81bbcb
Add drop functions for ranget
romainbrenguier Mar 7, 2019
e80340d
Unit test for ranget drop
romainbrenguier Mar 7, 2019
962c9f4
Use move in ranget constructor
romainbrenguier Mar 8, 2019
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21 changes: 20 additions & 1 deletion src/util/range.h
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Original file line number Diff line number Diff line change
Expand Up @@ -289,7 +289,8 @@ struct ranget final
public:
using value_type = typename iteratort::value_type;

ranget(iteratort begin, iteratort end) : begin_value(begin), end_value(end)
ranget(iteratort begin, iteratort end)
: begin_value(std::move(begin)), end_value(std::move(end))
{
}

Expand Down Expand Up @@ -341,6 +342,24 @@ struct ranget final
return begin_value == end_value;
}

/// Return an new range containing the same elements except for the first
/// \p count elements.
/// If the range has fewer elements, returns an empty range.
ranget<iteratort> drop(std::size_t count) &&
{
for(; count > 0 && begin_value != end_value; --count)
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💡 Could this be defined in terms of std::advance and std::distance? I think you could advance the begin iterator by the std::min of count and the distance between the begin and the end iterators.

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Maybe, but I don't know if it's worth it. Some distance functions work by iterating from the current position to the end, so using that plus advance would end up being less efficient.

++begin_value;
return ranget<iteratort>{std::move(begin_value), std::move(end_value)};
}

/// Return an new range containing the same elements except for the first
/// \p count elements.
/// If the range has fewer elements, returns an empty range.
ranget<iteratort> drop(std::size_t count) const &
{
return ranget<iteratort>{begin(), end()}.drop(count);
}

iteratort begin() const
{
return begin_value;
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39 changes: 39 additions & 0 deletions unit/util/range.cpp
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Expand Up @@ -57,6 +57,45 @@ SCENARIO("range tests", "[core][util][range]")
++it;
REQUIRE(it == filtered_range.end());
}

THEN("Drop first 2 elements")
{
auto range = make_range(list);
auto drop_range = range.drop(2);
auto it = drop_range.begin();
REQUIRE(*it == "acdef");
drop_range = std::move(drop_range).drop(1);
REQUIRE(drop_range.empty());
// Check the original is unmodified
REQUIRE(!range.empty());
REQUIRE(*range.begin() == "abc");
}
THEN("Drop first 5 elements")
{
auto range = make_range(list);
auto skip_range = range.drop(5);
REQUIRE(skip_range.empty());
// Check the original is unmodified
REQUIRE(!range.empty());
REQUIRE(*range.begin() == "abc");
}
THEN("Drop first 2 elements, move version")
{
auto range = make_range(list);
range = std::move(range).drop(2);
REQUIRE(!range.empty());
auto it = range.begin();
REQUIRE(*it == "acdef");
range = std::move(range).drop(1);
REQUIRE(range.empty());
}
THEN("Drop first 5 elements, move version")
{
auto range = make_range(list);
range = std::move(range).drop(5);
REQUIRE(range.empty());
}

THEN(
"A const instance of a `filter_iteratort` can mutate the input "
"collection.")
Expand Down